Snubbers are active hydraulic or mechanical devices designed to move freely under static loads while being able to absorb shocks of dynamic loads. Static loads are defined as slow varying loads where dynamic loads are defined as rapidly varying loads. Although these devices are theoretically desirable and widely used, they have proven unreliable in devices provide an alternative to snubbers.
Hydraulic frictional shock absorbers are disclosed in U.S. Pat. Nos. 2,929,507 (Thompson) and 3,054,478 (Rumsey). Thompson teaches a friction and fluid shock absorber wherein a number of successive shocks causes fluid to enter an outer portion of the piston thereby forcing a friction ring outward against the inner face of the cylinder. Rumsey discloses a friction hydraulic snubber wherein friction shoes are forced out against the barrel by action of a wedge shaped hydraulic piston, the load on the shoes varying accordingly with the velocity of the piston. The pistons return to their original position after the load has been removed by one or more springs. Hydraulic devices, however, are subject to leakage and valve problems, as well as corrosion, which inhibit proper movement.
Wedge-type frictional shock absorbers or resistors are disclosed in U.S. Pat. No. 3,796,288 (Hollnagel '288), 3,866,724 (Hollnagel '724) and 3,820,634 (Poe). These patents disclose the use of wedge-shaped internal friction structures to absorb the energy of a shock. Hollnagel '724 and Poe each employ a spring located around a moving piston to return the piston to its original position. Hollnagel '288 does not use a spring but rather utilizes a frictional wedge which is beveled on both sides, which cooperates with a V-shaped fixture about the piston. After compressive motion, the piston moves back to the original position by the opposing side of the V-shaped fixture contacting the opposing side of the wedge. Frictional shock absorbers have drawbacks including corrosion and contamination, i.e., oil, which causes inconsistent reactions to similar forces within the device.
A frictional brake type buffer device is disclosed in U.S. Pat. No. 3,603,577 (De Raad). The De Raad disclosure utilizes a spring and torsion bar to absorb the energy. The spring helps absorb energy and returns the piston to its original position while the torque in the torsion bar is applied to a pair of brake shoes, carried by the piston, which contact the interior of the cylinder to convert the remaining energy to heat.
Snubbers are, despite numerous problems in current design, extensively used in industry. One major area where such a device is used is in nuclear power plants where dynamic loads in piping are prevalent. Shock absorbers are necessary to support piping in nuclear plants which carries coolant fluid to and heated fluid (e.g. steam) away from the reactor, etc. Static load is seen in a nuclear plant setting during thermal expansion or contraction of the piping when the piping is exposed to variable temperature conditions. Dynamic motion is most easily seen during an earthquake. Here, many such shock absorbing supports are necessary and inspections, repair and replacements are very costly.
It is therefore a primary object of this invention to provide an axial frictional shock absorption device which minimizes piping dynamic motion while accomodating thermal expansion.
It is a further object of this invention to provide an axial frictional shock absorber which readily adjusts to changes in load arising from the force generated by shocks.
It is a still further object of this invention to provide such an axial frictional shock absorber which is both reliable and efficient.
It is a further object of this invention to provide an axial frictional shock absorber which is easy to install and replace existing snubbers.